The study compared the criminality of noninstitutionalized mentally retarded (NIMR) men and women in a Swedish birth cohort composed of 15,117 participants followed from before birth to age 30. NIMR participants were compared with non-mentally retarded (NMR) participants who had never been placed in a special class or institution for the mentally retarded nor admitted to a psychiatric ward. NIMR participants were more likely to have been convicted for a criminal offense before age 30 and for a violent offense (theft, fraud, narcotic offense, vandalism, traffic offense, and others). NIMR offenders had been convicted, on average, for the same number of offenses as NMR offenders. Among the NIMR offenders, 71 percent of men and only 43 percent of women were first convicted before the age of 18. Their childhood conduct problems were found to be associated with adult criminality. The between-group comparisons are probably generalizable only to countries with criminal justice systems, social welfare systems, child welfare agencies, and school systems similar to those in Sweden. Note, figure, tables, references